The second processing stage corrects the event coordinates for aspect drift and establishes the dispersion and cross-dispersion channel definitions, according to which the events and exposure are binned. This stage adds new attributes and columns to the EXPOSU0n and EVENTS tables of the combined event list. The aspect-drift corrections performed in this stage are specific to the chosen primary source. When spectra for other sources are constructed in the final stage, the inapplicability of these corrections introduces a systematic error, which is expected to be negligible in most cases. Nevertheless the user may wish to change the primary source (see task rgssources) and restart rgsproc here to obtain the most rigorously correct spectrum for a source other than the one originally designated as primary.